Method of manufacture of a drip irrigation hose

ABSTRACT

A drip irrigation hose of the continuous emitter type in which the outlets from the regulating passage each comprise a single longitudinal slit. By controlling the length of the slits and the flexibility of the film, water drips from the outlets when the hose is pressurized without clogging when the hose is depressurized. The slits are sufficiently long and the film is sufficiently flexible so the water drips from the outlets when the hose is pressurized. The slits are sufficiently short and the film is sufficiently rigid so the outlets close completely when the hose is depressurized. An outlet forming wheel has a knife blade on its periphery. A backing wheel engages the outlet forming wheel to establish a first nip therebetween. The backing wheel has on its periphery a circumferential slot into which the knife blade fits at the first nip. A rib forming wheel has around its periphery impressions that define a desired track pattern for the ribs. The outlet forming wheel and the rib forming wheel are mounted on a common shaft to operate in synchronism. A continuous strip of plastic film is directed in a path that reverses direction four times to accommodate these wheels.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/128,770,filed Aug. 4, 1998, now U.S. Pat. No. 6,464,816, which is a divisionalof application Ser. No. 08/850,407, filed May 2, 1997, which issued asU.S. Pat. No. 5,865,377 on Feb. 2, 1999, which is a continuation-in-partof application Ser. No. 08/650,469, filed May 20, 1996, which issued asU.S. Pat. No. 5,634,595 on Jun. 3, 1997, which is a continuation ofapplication Ser. No. 08/279,813, filed Jul. 19, 1994, which issued asU.S. Pat. No. 5,522,551 on Jun. 4, 1996.

BACKGROUND OF THE INVENTION

This invention relates to drip irrigation and, more particularly, to adrip irrigation hose with an improved outlet construction and a methodfor its manufacture.

Drip irrigation hose can be classified into two types—hose havingdiscrete emitters and hose having continuous, integral emitters. Anexample of a drip irrigation hose having discrete emitters is shown inU.S. Pat. No. 4,850,531. An example of a drip irrigation hosecontinuous, integral emitters is shown in U.S. Pat. No. 4,247,051. Dripirrigation hose having continuous integral emitters offers thepossibility of lower cost and ease of manufacture and installation.

The design of the inlets to and outlets from the emitters is critical.If the effective outlet area of the emitters is too large, dirt anddebris can collect externally in the outlets, thereby causing externalclogging. If the effective inlet and outlet areas of the emitters aretoo small, they become clogged internally and cease to serve theirpurpose. Further, if the effective outlet areas of the emitters are toosmall, water squirts out of the hose instead of dripping, and soilerosion results.

U.S. Pat. No. 4,247,051 discloses a drip irrigation hose formed bybending a strip plastic film along its length to form an overlappinglongitudinal seam between opposing longitudinal margins of the film.First and second longitudinally extending, laterally spaced, transverseribs interconnect the opposing margins along their length to seal theoverlapping longitudinal seam. The ribs are formed by one or more moltenplastic beads extruded onto the film. As a result, a flow regulatingpassage is defined by the ribs and the opposing margins and a supplypassage is defined by the remainder of the film. Water flows from thesupply passage to the flow regulating passage through a plurality oflongitudinally spaced inlets. Water flows from the flow regulatingpassage to the exterior of the hose through a plurality oflongitudinally spaced outlets longitudinally spaced from the respectiveinlets to provide a substantial path length from each inlet to arespective outlet. In one embodiment, the outlets each comprise twoparallel slits that form between them a flexible flap. The flap servesas an outlet valve, opening and closing as the hose is pressurized anddepressurized. However, unless the plastic film is very thick and rigid,the flaps do not close consistently when the hose is depressurized andtherefore, the outlets can become clogged by soil drawn into the slits.

A problem encountered in the manufacture of continuous emitter dripirrigation hose is coordinating the position of the outlets and thetrack pattern of the ribs. If care is not taken, the track pattern ofthe ribs may overlap the outlets, and thereby cause the outlets to be onthe high pressure side of the flow regulating passages.

SUMMARY OF THE INVENTION

One aspect of the invention is a drip irrigation hose of the continuousemitter type in which the outlets from the regulating passage eachcomprise a single longitudinal slit. By controlling the length of theslits and the flexibility of the film, water drips from the outlets whenthe hose is pressurized without clogging when the hose is depressurized.The slits are sufficiently long and the film is sufficiently flexible sothe water drips from the outlets when the hose is pressurized. The slitsare sufficiently short and the film is sufficiently rigid so the outletsclose completely when the hose is depressurized.

Another aspect of the invention is a method for making a drip irrigationhose having longitudinal single slit outlets and/or inlets. A firstoutlet and/or inlet forming wheel has one or more knife blades on itsperiphery. A second backing wheel engages the first wheel to establish afirst nip therebetween. The backing wheel has on its periphery acircumferential slot into which the knife blade fits at the first nip. Athird rib forming wheel has around its periphery impressions that definea desired track pattern for the ribs. A second nip is established with athird wheel in which the desired track pattern is formed. The first andsecond wheels are mounted on a common shaft to operate in synchronism. Acontinuous strip of plastic film is directed in the following path inthe order recited. The film is wrapped around the second wheel toreverse direction and pass into the first nip, thereby forming theoutlet slits. The direction of the film is reversed leaving the firstnip to transport the film toward the first wheel. The film is wrappedaround a portion of the periphery of the first wheel spaced laterallyfrom the knife blade to reverse direction. The direction of the film isreversed to transport the film toward the third wheel. The film istransported under an extruder to deposit a bead of molten plastic on thefilm before the third wheel. The film is transported into the second nipto form the desired track in the molten plastic. After the film leavesthe third wheel, the hose is finished. The described method forms theoutlet slits and the track pattern in a coordinated fashion. As aresult, the outlets are not restricted or plugged by the ribs.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of specific embodiments of the best mode contemplated ofcarrying out the invention are illustrated in the drawings, in which:

FIG. 1 is a schematic block diagram of the method for making a dripirrigation hose of the continuous emitter type;

FIG. 2 is a schematic view of a portion of the film path for making adrip irrigation hose in accordance with the invention;

FIG. 3 is a schematic view of a portion of the film path in analternative embodiment to the film path of FIG. 2; and

FIG. 4 is a side partially cutaway view of a length of drip irrigationhose incorporating the principals of the invention.

FIG. 5 is a schematic diagram of apparatus for completing themanufacture of a drip irrigation hose following the operations shown inFIG. 2.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENT

The disclosures of U.S. Pat. Nos. 4,247,051, 4,984,739 and 5,123,984 areincorporated fully herein by reference.

The drip irrigation hose of the invention is made from a continuousstrip of flexible, water impervious plastic film, generally ranging inthickness between 4 and 15 mil. As depicted by block 10 in FIG. 1,outlets and/or inlets are formed in the strip of film along one margin.As described in more detail below, each outlet and/or inlet comprises asingle longitudinal slit in the film. Next, as depicted by block 12, twomolten plastic beads made of material compatible with the film aredeposited by an extruder on the margin of the film on either side of theoutlet slits.

Next, as depicted by block 14, the track pattern of the ribs is formedin the molten beads by a rib forming wheel. The track pattern isrepeated each time the rib forming wheel completes a revolution. Asdepicted by block 16, after the ribs are formed, the margins of the filmare overlapped to position between them the track pattern. Finally, asdepicted by block 18, the overlapping margins are sealed by the stillmolten ribs to form the finished hose. The described steps, except forformation of the outlets and/or inlets, are shown in more detail in thereferenced '984 patent. Alternatively, either the inlets or the outletscould be formed as interruptions in one of the ribs.

FIG. 2 illustrates the path of a continuous strip of film 38 from whichthe drip irrigation hose is made between the formation of the outletsand/or inlets (block 10) and the formation of the track pattern (block14). An outlet forming wheel 20 and a rib forming wheel 22 are mountedon a common shaft 24 to synchronize their operation. Wheels 20 and 22have the same diameter. A backing wheel 26 engages outlet forming wheel20 to establish a nip 28 therebetween. A knife blade 30 is mounted onthe periphery of wheel 20. Wheel 26 has a circumferential slot 32 intowhich knife blade 30 fits at nip 28. Direction changing wheels 34 and 36also define part of the film path. Wheels 20, 22, 26, 34, and 36 haveflanges to guide film 38 laterally during the manufacturing operation.

Wheel 22 has, around its periphery, impressions that define the desiredtrack pattern 24, for example, one of the track patterns shown in the'051 patent or in the '739 patent. The direction of movement of film 38is depicted by the arrows in FIG. 2. Film 38 is wrapped around wheel 26to reverse direction and pass into nip 28. As a result, a slit is formedin film 38 each time blade 30 passes into nip 28. A slit is formed eachtime wheel 20 completes one revolution. After leaving wheel 26, film 38is wrapped around wheel 34 to reverse direction and return toward wheel20. Film 38 is wrapped around a portion of the periphery of wheel 20,spaced laterally from knife blade 30, to reverse direction. Afterleaving wheel 20, film 38 is wrapped around wheel 36 to reversedirection and move toward wheel 22. Wheel 36 could be canted slightly toprovide a smooth transition in the film path between wheels 20 and 22,and the film could twist slightly between wheels 36 and 22. Betweenwheels 36 and 22, film 38 passes under an extruder 40 which deposits oneor more molten plastic beads on one margin of film 38. Since wheels 20and 22 are mounted on a common shaft, the formation of the outlets andthe track pattern is coordinated and their relative positioning isclosely controlled. After leaving wheel 22, film 38 is finished in themanner illustrated in FIG. 5. More specifically, as film 38 approachesextruder 40, its inner margin is folded over and extruder 40 forms oneor more beads 42 on the exposed surface of the inner margin of film 38.A backing wheel 60 underlies wheel 22, which has track pattern 24. Afterpassage through the nip formed by wheels 22 and 60, the outer margin offilm 38 is folded by a guide 62 to overlap the inner margin of film 38.The folded film 38 then passes through the nip of a form wheel 64 and abacking wheel 66. Form wheel 64 has a groove 68 that depresses the beadsto set the bead height at a specified value. The value of the beadheight determines the flow rate of the hose. A finished hose 70 leavesthe nip between wheels 66 and 68. In a typical embodiment, the diametersof wheels 20 and 22 would be about from 3 to 6 inches, the diameter ofwheel 26 would be about 4 inches, the diameters of wheels 34 and 36would be about 4 inches, and the distance between wheels 22 and 36 wouldbe about 24 inches.

If the inlets also comprise slits another knife blade is mounted on theperiphery of wheel 20 laterally spaced from knife blade 30 and wheel 26has another circumferential slot laterally spaced from slot 32 intowhich the other knife blade fits. The inlets as well as the outlets areformed as the respective knife blades pass into nip 28.

FIG. 3 illustrates an alternative film path arrangement that permitswheels 20 and 22 to have different diameters so that the outlet spacingcan be greater than the track pattern length, which produces a skip inthe outlet configuration. Wheel 20 and a toothed wheel 50 are mounted ona shaft 52. Wheel 22 and a toothed wheel 54 are mounted on a shaft 56. Atoothed belt 58 couples wheels 50 and 54 to synchronize the rotation ofwheels 20 and 22 in a ratio to cause the desired skip in the outletspacing relative to the track pattern length. In short toothed wheels 50and 54 and toothed belt 58 replace shaft 24 in the embodiment of FIG. 2.The diameters of wheels 20, 22, 50, and 54 are selected so the angularvelocity of wheel 22 is a multiple of the angular velocity of wheel 20,depending upon the desired outlet skip. As a result, the same ribforming wheel 22 can be used to produce a variety of outlet spacings,i.e., skipped outlet configurations.

In FIG. 4, the completed drip irrigation hose is shown. Strip 38 is bentalong its length to form an overlapping longitudinal seam between aninterior margin and an exterior margin of the strip. Spaced apart,transverse ribs 42 and 43 extend longitudinally through the seam toconnect the margins of strip 38, forming a seal and a flow regulatingpassage 44 therebetween. A water supply passage 45, having a much largercross-section area then flow regulating passage 44 is defined by theremainder of strip 38. Longitudinally spaced apart slits 46 in theportion of strip 38 between supply passage 45 and flow regulatingpassage 44 serve as inlets to flow regulating passage 44. Longitudinallyspaced apart slits 47, formed in the exterior margin of strip 38, serveas outlets from the hose. Slits 47 are displaced from the respectiveslits 46 to provide a substantial path length from each inlet to arespective outlet. Preferably, cross ribs 48 are employed to divide theflow regulating passage into segments, such that slit 46 is at one endof the segment and a slit 47 is at the other end of a segment.Alternatively, the inlets could be formed by interruptions in rib 42 asillustrated in FIGS. 5 and 6 of the '051 patent and as illustrated inthe '739 patent. The shape of ribs 42, 43 and 48 are determined by thetrack pattern on wheel 22 (FIG. 2). Preferably, chevrons are formed onthe adjacent interior surfaces of ribs 42 and 43 to create turbulentflow in the flow regulating passage as illustrated in the '739 patent.

By controlling the length of the slits and the flexibility of the film,water drips from the outlets when the hose is pressurized withoutclogging when the hose is depressurized. Typically, the line pressure ofthe water used for crop irrigation ranges from about 4 psig to 14 psig.Slits 47 are sufficiently long and strip 38 is sufficiently flexible sothe water drips from the outlets when the hose is pressurized, ratherthan squirting. The effective area of the outlets remains small becausethe material on both sides of the slits remain in the same plane, ratherthan buckling. If the slits are too short or the strip is too rigid, thematerial on either side of the slits does not move sufficiently to makea large hole when the hose is pressurized and water squirts out the hoseand erodes the soil. Slits 47 are sufficient short and strip 38 issufficiently rigid so the outlets close completely when the hose isdepressurized. If the slits are too long or the strip is too flexible,the slits do not close when the hose is depressurized. Typically, theslits are about ¼ inch for a 4 mil film thickness and the slits areabout ⅜ inch for a 15 mil film thickness. Thus, if the slits are muchshorter than about ¼ inch for a 4 mil film thickness or if the film ismuch thicker than about 4 mil for a slit length of about ¼ inch, thewater may squirt from the outlets. Similarly, if the slits are muchlonger than about ⅜ inch for a 15 mil film thickness or if the film ismuch thinner than about 15 mil for a slit length of about ⅜ inch, theoutlets may not close after the hose is depressurized.

Despite the foregoing, it has recently been discovered that with a slitlength of almost one inch, the outlets still close after the hose isdepressurized if the film is flexible enough.

The described embodiment of the invention is only considered to bepreferred and illustrative of the inventive concept; the scope of theinvention is not to be restricted to such embodiments. Various andnumerous other arrangements may be devised by one skilled in the artwithout departing from the spirit and scope of this invention.

1. A method for making drip irrigation hose comprising: rotating anoutlet forming wheel having a knife blade on its periphery; positioninga backing wheel to engage the outlet forming wheel and establish a nip,the backing wheel having a circumferential slot into which the knifeblade fits as the outlet forming wheel rotates; moving a strip ofplastic film through the nip to form single slit outlets repeatedlyalong the strip as the knife blade rotates; forming on the strip anelongated flow regulating passage; and forming inlets to the flowregulating passage that are spaced from the outlets to form asubstantial path length from each inlet to a corresponding outlet,wherein the outlets couple the flow regulating passage to the exteriorof the hose.
 2. The method of claim 1, wherein the strip of plastic filmhas first and second margins, and wherein the method further comprisesoverlapping and sealing the first and second margins to form a tube fromthe strip of plastic film.
 3. The method of claim 2, wherein the flowregulating passage lies between the overlapping margins.
 4. The methodof claim 1, wherein the step of forming a flow regulating passageoverlaps and seals margins of the strip between the inlets and theoutlets, wherein the outlets couple the flow regulating passage to theexterior of the hose.
 5. The method of claim 1, in which the outletforming wheel is rotated such that the knife blade forms slits thatclose completely when the hose is depressurized.
 6. The method of claim5, in which the strip is flexible, additionally comprising partiallywrapping the strip around one of the wheels as the strip moves throughthe nip.
 7. The method of claim 1, in which the strip is flexible,additionally comprising partially wrapping the strip around one of thewheels as the strip moves through the nip.